Clinical analyzers conventionally use an aspirator probe to aspirate sample into a disposable tip, and then dispense some of that sample onto a slide element that has dried reagents therein. Such a sequence is schematically illustrated in, e.g., U.S. Pat. No. 4,340,390, FIG. 2 thereof. It is also conventional to provide for some compliance in the horizontal mounting of the probe, to allow for slight displacement errors in the seating of the tip at, e.g., the sample-dispensing station. Such compliance is conventionally achieved using a vertically depending, pivotable spring a short distance above the seating surface of the tip, the spring allowing for the horizontal displacement.
Such a design has worked well in most instances. However, occasionally there is a problem due to the amount of horizontal displacement incurred at the sample dispensing station. Although structure is provided to accurately "seat" the tip for dispensing, notwithstanding such displacement, when the tip starts to withdraw, the displacement force, still present, acts to slightly pivot the tip above its vertical axis. I have discovered that if, as with some chemistries, the dispensed sample has not been completely absorbed, this pivoting can lead to what is called "tip flick". That is, the residual liquid above the surface of the slide is flicked off center, causing the slide to "read" as though the dispensing occurred off-center. Such off-center locations of the sample can interfere with accurate detection of the concentration of the analyte in question.
Accordingly, prior to this invention there has been a need to prevent "tip flick" by some mechanism.